Aircraft landing gear lock



Oct. 12, 1948. J. E. wEscoTT AIRCRAFT LANDING GEAR LOCK 2 Sheets-Sheet 1 Filed July 17, 1945 INVENTOR.

Oct. 12, 1948. J. E. wE'scoT-r AIRCRAFT LANDING GEAR LOCK 2 Sheets-Sheet 2 Filed July 17, 1945 INVENTOR..

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Patented Get. 12, 1948 AIRCRAFT LANDING GEAR LOCK John E. Wescott, Hagerstown, Md., assignor to Fairchild Engine and Airplane Corporation, a corporation of Maryland Application July 17, 1945, Serial No. 605,523

9 Claims. 1

The present invention relates generally to landing gears for aircraft and similar vehicles, and more particularlyto improvements in mechanism for locking and securing the pivoted joints of such landing gears in their operative positions.

In the design of modern high performance airplanes of the land type, retractable landing gears are almost universally provided to withdraw the wheels into the aircraft body or wing to reduce their resistance in flight, and in such landing gears, it frequently becomes expedient to utilize struts of the so-called breaking type. A strut which is pivoted or articulated between its terminals to facilitate its being folded with respect to its parts, in addition to the swinging pivotation about its upper terminal, has generally become known in the art as a breaking strut. In such breaking strut landing gears, it is of utmost importance that the strut which breaks in retraction is securely locked against inadvertent collapsing or foldin in its extended operative position, particularly when subjected to shocks and impacts incidental to landing or running over rough terrain.

A further consideration of importance is the necessity that the locking means for such struts be so timed in its operation that it permits the breaking strut to become fully extended and aligned before the lock is applied, and also to unlock the strut immediately before the retractive force is applied to the landing gear. Heretofore, many efforts have been made to lock landing gears, and particularly the breaking struts thereof, but those devices which have been used most commonly were generally of the latch or axially movable pin type, frequently requiring spring actuation and usually of cumbersome construction. Most of these prior devices have been susceptible of bein obstructed and impaired by operation on muddy or otherwise unsurfaced landing fields, and have frequently been placed out of adjustment and have otherwise failed to operate satisfactorily under continental service conditions.

The present invention is directed to an improved type mechanism comprising essentially three sets of hinged links of equal length separately articulated to the breaking strut retracting mechanism and a lost-motion device to provide proper timing of the lock. The present invention also embodies an improved yoke type construction for attaching the upper terminal of the breaking strut to the aircraft structure, the provision of an improved retracting mechanism and lock actuating device as well as a quick make-and-break double acting spring device to snap the locking linkage into and out of its looking condition across the dead-centers of the locking pivots.

It is accordingly a major object of the present invention to provide an improved lock for a retractable landing gear. A further object resides in the provision of a simplified fool-proof locking mechanism which does not require the use of reciprocatin latches or axially movable pins. A further object of this invention resides in the provision of a breaking strut lock which is made operative or inoperative concurrently with the retraction of the landing gear assembly and accomplishes such locking function automatically by the pivotation of the several links of which it is comprised, A further object lies in the provision of a novel lost-motion device to insure positive locking and unlocking properly timed with respect to extension and retraction of the gear. This invention also has for one of its objects the provision of a novel and advantageous retractable landing gear arrangement, including the actuating and lock initiating mechanisms, both with respect to its general organization and the details of its several parts.

Other objects and advantages of the present invention will become apparent to those skilled in the art after reading the present specification as taken into consideration with the accompanying drawings forming a part hereof, in which:

Fig. 1 is a side elevational View of a preferred form of the present invention as applied to a retractable landing gear attached to the wing of an airplane;

Fig. 2 is an elevational view of the landing gear assembly as taken along the lines 22 of Fig. 1 looking forward;

Fig. 3 is an enlarged detail view of a lost-motion device associated with a fixed strut of the landing gear;

Fig. 4 is a plan view of a portion of the retracting mechanism and the lock actuating device;

Fig. 5 is a side elevational view of the mechanism and device shown in Fig. 4, as taken along the lines 55 thereof;

Fig. 6 is an enlarged detail view of the articulated portion of the breaking strut and its associated lockin mechanism; and

Fig. 7 is a sectional view looking downwardly upon the articulated strut and locking mechanism of Fig. 6 as taken along the lines thereof.

Referring now. to Figs. 1 and 2, the numeral [0 indicates the main shock absorbing strut of a 3 landing gear and comprises a lower shock-absorber wheel-carrying portion Hla to which is rotatably mounted the ground-engaging wheel I l, the upper part of the portion Illa being rigidly attached, as by the fitting Illb, to the upper tongue portion [00. The latter portion Ind is pivotally mounted or articulated byv means of the transverse=liorizontal pin E 2 7 upon the arms orbi .furcations [3a of a yoke member I3, this yoke and the strut l 0, hinged by the pin l2, comprising thev breaking strut and joint of the type heretofore referred to.

The arms Hia of the yoke l3 are intermediately interconnected by a tubular'tie ISbof integral construction and embrace the upper end'ofthe strut portion lflb which terminates in an angularly cut portion Inc to which are-integrally at tached or welded the plates Hid, to be hereinafter more fully described. The upper portion of the arms 13a of the yoke are connected by the cross tubular assembly l4carrying integral lugs ld'd apertured to-- receive the-hinge pins i5'by' which the yokeispivota'lly attached to the rear' spar I6a of the win 1'5.

A ri'gidinclined dragstrut' 11 f fixed length ispivotallyconnectedtothefront wing spar [6b bythe-pivot pin l8-at itsupper forward end and is-.-'pivotally-connectedby the pin l9 at its lower rearward end -through' a fitting integral with the loweriwlieel carrying-portion; Ella of @thestrut L9. The landing gear arrangement shown in Fig: 1,

as selectedfor 'explanatory' purposes, is retracted upon counterclockwiserotation of the drag strut H; about it's-pivot 1&3 serving to-rearwardly break the main-strut l'll' anditsyok e member [3' at its' articulated-joint l 2-; such that the landing wheel is drawn upwardly in a substantiallyvertical direotion;

Asindicated in Fig. 1" the mechanism for retracting the land-ing-gear is comprised'of a torque shaftm? preferably coupled-tea suitable motor or- 'other'source of rotary-power (not shown), the shaft beingu-niversally coupled at 2i" to a gearbox 22 provided with a horizontally extending low speed s-haft 2 3i: It'includes a'triangula-r driving frame 2425-26 which is suitabl'y keyed or fastened-toithe shaft-2'3; ancl'comprises a rigid frame consisting-of a strut-retractingcrank 24 and the? lock-*actuatin'g crank 2 each fixedly attached to each other andthe shaft 23 at their inner inter secting= ends and'tied togetherat their outer ends bythe member 26; The lower outer terminals of is articulated the actuating link 2 8 the lower terminal clevis 28a of which is pivotally attached'to a lost-motion" device 3ilg1w-hibhis shown in detail inFi'g'i-3L Referring now to the latter figure, bracket portionsfl'lr are welded'or otherwise attached to the central portion ofthe drag strut I1 and provide journals for the pivot 32, which is offset from; but :ext'endsparall'el to; the inclined longitudinal axis of the dragstrut. rocker element 33pmvided: with?adjustable-contacts 33d and 331)- at 7 direction about the pivot l2, and the 4 7 ing the degree of lost-motion through which the actuating rod 28 may move before it applies its force directly to the drag strut.

The lock actuating mechanism is rotated simultaneously with the retracting strut mechanism and from the same gearbox ZZ'by means of a cam 27 which is rigidly'supported at the intersection of: the cranlo 253 and thexcrossa frame! member 26. A complementary cam element 36 is fixedly attached to a lever bracket 35 in turn mounted upon the pivot assembly 36 attached to the rear spar: Eta by" means of the bolts 36a. The cam 36., is such that it is engageable by the cam 2'! in both further clockwise movement of the arm 25 fronr the position shown in Figs. 1 and 5, or as well'as any counterclockwise movement from this position. Than-adjacent portion of the pivotal assemblyi36, pivotally mounted upon the brackets 3?, there is fixedly attached an arm 38 pivotally connected by the pin 39 to the link ll of the dowrrlock-assembly 4B;

The link 4| ispivotally connectedto-a lever- 6- Z by means of the pivotal-connection 43 the lever iz being pivotally-mounted upon the abovementioned pivot l Eof the'landing' gear yoke and provid'ed at its-outer extremities with a pivotal-conneetion't 'to afurtherlink 45 of irregular conformation toclear-thecross tie lfi of the yoke asthebreaking strut is folded upwardly upon itself; pivotally-connected by thepi-n 46 -170 an arm Nb of the link tl-l which i's'intermediately braced by the cross tie element-47c as more particularly shown" in detail in Fig. 75 A similar link 48'is provided on the opposite side of the extended axis of thestr-ut HJ, being similarly provided with an arm portion 48b and a bracetie sea. The tri-j angularframework of the links 4? and Glitter minate in apicesat their outer extremities-on" which they'areprov-ided with fittings embracing V the 'common'pivot pin 49 -to whichiis also pivotally connected an intermediate central link or arm: 50 of the same length as links M and 48.

These outside triangular links ll and Mi -are pivotallym'ounted as-by-thepins 5i and 52 re- The central link 50, connected" Referring to both Figs. 6 and 7 which show--in full line the locked position of the breaking strut, it will be noted thatin this locked position the axes: of the pivot pi-ns fi i, 52=and 53 are transversely aligned alonga common axis which has been 'de'si'gnatedinFig. 6-as axis B which together withtheparal1elaXis lZ'being the axi of articulation of-thebreaking strut, serves to define the straight line A'IB--C' into which thelinks 61-; emanate may be rotated in'a counterclock-' wise direction in suchmanner that the pivot 59 isrot'ated'to the point Cat 'which the strut I0 iscapable of being folded or rotated in-a clockwise yoke as folded:in-the"opposite direction. r

Further referringto'Figs. Sand 7; there is pivotally connected to the outer arms 47b and :181), as by the pivot 51", a doubletension springf i having terminal fittings a-nd fifi pivotally mounted re spectivelyat' 5-1 on the swinging linkages li-Tand Q8; and at the pivot 5'8'upon theyoke member l3} The spring unit'54 serves as a quick-acting V a resilient element to snap the links M and 148- intothei-r. locking position--as the pivots" 58-, 52%

The lower end of the curved link'dfi -is';

and 5! proceed beyond the dead-center position after the gear has been fully extended and during the succeeding locking cycle. A further important purpose of the springs 54 is to hold the locking links in an unlocked position in case there is a time lag between the disengagement of the cams 21 and 34 and the start of the retraction of the landing gear due to the rocker 33 not having as yet engaged the stop He at the same instant that the cam becomes disengaged. In other words, the quick-acting spring mechanism serves to maintain the landing gear locking mechanism from dropping into its looking or binding condition as soon as the cam 34 may have disengaged but prior to the application of a positive reacting force by the actuating link 28 upon the drag strut ll initiating folding of the breaking strut. The further application of the retracting force to the drag strut will continue to break or fold the main strut about its pivot axis l2 and to move the axis of the pin 53 downwardly out of alignment with the line AB-C.

It will accordingly be noted that clockwise rotation of the low speed shaft 23 of the actuating gearbox 22 causes extension of the landing gear from its retracted position by permitting the gear to drop by gravity, and during this down cycle the rocker 33 remains in the same 'position as during the upward or retracting cycle referred to above in which the stops 33a and Ho are in contact, being held statically in this relationship due to the weight of the landing gear pulling against the actuating mechanism, and due also to the retarding or braking action of the gearbox 22. It will also be apparent that the landing gear cannot be locked until it has reached the fully extended or down position. This is automatically taken care of by the lost-motion rocker 33 which insures that the landing gear be at its extreme down position before the links swing into their locked position. It is similarly apparent that the landing gear cannot be retracted before it is unlocked and the rocker assembly 33 also insures that the retracting driving frame 2425-2E is rotated slightly in a counterclockwise direction to initiate unlocking of the linkages 4?, 48 and 50 during the period in which the rocker 33 in Fig. 3 rotates from the position shown in which 331) and Nb are in contact, to the position in which 33a and He would be in contact, and the lifting force is applied directly from the actuating link 28 to the drag strut H. The lost-motion assembly 33 also provides an additional distinct advantage in that it permits both the landing gear retracting mechanism and the locking mechanism to be actuated from the same gearbox and the same power source.

As indicated above, clockwise rotation of the gearbox shaft '23 and the frame 24-25-26 causes extension of the landing gear from its retracted position during which period the weight of the gear pulls against the lagging or braking gearbox and the rocker is in the opposite position to that shown in Fig. 3. During the latter portion of this extending or down cycle of the driving mechanism the cam 2! engages the cam 34 and the locking linkage is gradually rotated from its dotted position C in Fig. 1 toward the full line position of this figure. Immediately after the landing gear reaches the down extremity the simultaneous engagement of the cam serves to drive the links beyond the previously referred to dead-center position of the pivots 58, 52 and 5 1 beyond which the quick-acting spring 54 snaps the links into the locked position and 7 landing gears.

the rocker 33 is permitted to rotate freely in a direction which disengages the rocker portion 33a from the stop He and rocks it into the position shown in Fig. 3 in which the mechanism is left in a condition to again start upon the following up cycle. As indicated in Figs. 1 and 6, a limit switch 59 of the micro-switch type is fixedly attached to the upper portion of the main strut part lflb with its movable element in a position where it is contacted by the linkage 48 such that use may be made, in a well known manner, of the making or breaking of the electrical contact to stop the source of power at the end of the down cycle, to provide a suitable signal or indicator for the operator that the gear is in the locked position, or to initiate or actuate a signal.

The present specification and drawings have been directed to a single preferred embodiment of this invention for purposes of simplifying its description and explanation, but it is contemplated that the essential features of the present invention are adapted for use in other landing gear arrangements and in other than aircraft Such other forms andmodifications of the present invention as may occur to those skilled in the art after reading the present specification and drawings are intended.

to fall within the scope and spirit of this invention as more specifically set forth in the appended claims.

I claim:

1. In an articulated joint, the combination of pivotally connected joint members, onev of said members extending to a terminal longi-.

tudinally displaced from said pivotal connection, a locking device comprising pivotally connected links each pivotally mounted respectively on one of said joint members on the same transverse axis in the region of said extended mem-.

ber terminal in the aligned position of said joint members. and means for moving said links to displace the axis of their pivotal interconnection from the plane defined by the axis of their pivotal connection to said respective joint members and the axis of pivotal interconnection of said joint members for the locking of the saidarticulated joint and for placing the axis of the.

pivotal interconnection of said links in the same said plane but remote from the axis of pivotal interconnection of said joint members for the unlocking of said members.

2. In a breaking strut, the combination of a pair of pivotally connected strut halves, said strut halves overlapping beyond the transverse plane of said pivotal connection, a locking mechanism comprising at least two pivotally connected links each pivotally mounted respectively on one of said strut halves in the region of their overlapping portions at one terminal of each link and pivotally connected to each other at their opposite terminals, the said pivotal connection of said links to said strut halves being axially aligned and parallel to the strut pivot and the pivot of said first link terminals and means for rotating said links about the axes of their pivotal connections to said strut halves until said axes and those of the said pivotal interconnection of said link terminals and of said strut halves lie in the same, plane in a parallel relationship but not in axial alignment therein to permit unlocking movement of said strut halves.

bination of pivotally connected strut members adapted-when aligned :toassist-in the support :of said" aircraft, one of sai-dastrut "members :extendingto a terminal longitudinally displaced =ifrom said pivotal connection .to theother .said. strut member, :a l locking :device comprising pivotally connected links of equal length each pivotally mounted respectively'on one of said strut members-on-the same transverseaxis in the region of maid-extended :strut member terminal with their-pivotal axes in alignment awhenuthe said strut members are aligned, and means f-or :moving ;the=said links to-idisplace the :axisiofrtheir pivotal interconnection ithereof f-romnthe :pla-ne defined by the-axis of apivotal interconnection of the said strut members and the pivotal connection of the remaining link terminals ithereto for the locking of the strut imembers, and for placing-the axis of their pivotal; interconnection ins-the same said plane. but remote from the axis of pivotal interconnection of said strut members :f-or the unlocking: of said strut members.

A. "Imam-aircraft strut, a wheel-carrying Estrut portion,- a :yoke strut portion pivotally mounted uponasupporting aircraft structure at its .-upper terminal and pivotally :embracing the said wheel-carrying strut-portion adjacent the lower terminal of said yoke strut :portion the upperiterrurinal-of said wheel-carrying strut portion extending upwardlybeyond thesaid-p-ivotal connection to-isaid. yoke strutlportion, a pair of laterally spaced links of equal length eachpivotally interconnected at their outer terminals extendingzlaterally fromsaid strut upon a common pivotal. axis 1 and. separately pivotally 1 connected toasaid yokestrut portion. at their inner terminals:inwthearegionnof :the upper terminal; of-said wheel-carrying strut portion, a link member pivotally interconnected with said common OIHGIPEDilL-Oli vintermediate said first links and piuota-llyconnec-ted. to :aniu-pper terminal of said wheel-,carryinglstrut portion in alignment with saidzoipiuotiaxes of said strut when said yoke-and wheel-carryinghstrut portions are in operative alignment, andmeansuassociated with one of saidwlaterally spaced -.links .torotate all three such into'positionslzlaterally. of .said strut forrlocking and unlocking. said'alrcraft strut portions.

-5. in 1a retractableylanding gearfor aircraft, a main strut of the breakingutype comprising a lowervwlheehcarrying:.portion and an :upper yoke portion pivotally articulated :thereto, said yoke portion -beingxpivotally connected to the-aircraft structure at its zuppertermina'l, a drag strut pivotailly-..connected to the aircraft structure on an 7 axisspaced from .said yoke :pivot connection to then-lrcraft structure and :pivotally connected I at itsopposi-te terminal .toisaiid wheel. carrying (strut portion a plurality of .linksppivotally interconnected to-each other and separately-tosaidibreak- I iugrstrut portions on aligned .axeslinthe ailigned condition Of5.;S2Lid strut portions adapted for-the locking of said strut portion-s inn-the Laligned extended position of :said breaking strut :by. preventing: their .saiid pivotal articulation; and actuating means 1 l-operatively connected :to both said drag striutiand said locking means for the extension of saiddrag: strut-and said main strut portions into theirqalignedpositionsand-the locking of said breaking strut portions.

i :5. ln a retractablelanding gear tor aircraft a main strut of vthe breaking ,typebOmprising lower wheel-carrying portion and an upper, yoke portion pivotally articulated thereto, said yoke portion being pivotally connected to the aircraft structure at its upper terminalpadrag strut pivot ally-connected to the aircraft structure on anraxis spaced from said yoke pivot connection ..to--' the aircraft structure and pivotally connected atits opposite terminal to said Wheel-carrying portion, anplurality of links-pivotally interconnected" to each-other and separately to :said breaking strut portions on aligned-axes in the aligned condition of said' strut-portions=adapted for-the locking of said 'strut portions in the aligned extended'posi tion of said breaking strut .by-preventingthe-said pivotalarticulation of its said strut portions, lostmotion means interposed between said I locking means and said drag strut, and actuating means operatively connected to both said drag strut through said lostmot-ion means and to said lockingineans for the initialextension of said landing gear-rand the subsequent locking of said breaking strut portions.

*7. In aretractableaircraft landing gear includinga breaking leg-strut pivotally connected at its upper terminaltothe aircraft structure and rotatably carrying a ground engaging wheel =at-i ts lower tenninaL-a drag strut pivotally connected to said aircraft structure and'to said breaking strut at its lower portion, aplurality of lockinglinks of equal length pivotally interconnected to each other at adjacent terminals of each andre spectively to each portion of-said breaking strut on aligned axes inthe operative condition of said breaking strut, said locking links adapted when disposed such that all of their axes are parallel but not coincidentalto permit unlocking of said breaking strut portions, and-common power means for the rotation of said locking links about theaxes of their pivotal connections to said initial unlocking subsequent 'retra'ction vmeans pivotally interconnected at adjacent ends and pivotally connected respectively :tothe' said 7 V yoke and Wheel-carrying strut; portions at the opposite end of'each, a drag strut -pivotally -inter+ connected between said aircraft structure and said wheel-carrying strut portion, -mechanis'm connected to saidlocking device adapted for its rotation about its pivotal connection to said struts in theiroperative position into-locking andfune locking conditions of said-breaking strut,:a lostlmotion device-associated 'with-said-drag strut; V actuating linkage connected to said lost-motion device, rotary power I means adapted for; concurrent engagement with saidactuating linkage and said-lock actuating mechanism whereby rotation of powermeans initially "unlocks said breaking strut' prior to said actuating links'overcoming 7 said locomotion device andapplying'retractive force to said drag strut. 9. A retractable landing-gear for aircraft comportion pivotally attached to'the aircraftpand a lower Wheel-carrying strut portion articulated prising a breaking strut including anupperyoke thereto, locking means including plural links pivotally interconnected at adjacent ends and. pivotally connected at their other'ends respectively' to the-said yoke and wheel-carrying' strut portions,.sai'd locking means rotatablein'the operative position of said strut portions from -a'-1o-cked to .an unlocked position. acrossiansintermediate dead-centerpositiom adrag strut piuotallyinteri-fl connected to said aircraft structure and to said wheel-carrying strut portion, lock actuating mechanism connected to said locking means adapted for its rotation into locked and unlocked conditions of said breaking strut, a quick acting tension device pivotally interconnected to said locking means and said strut yoke portion for holding said locking means in either position beyond its dead-center position, lost-motion mechanism associated with said drag strut, retraction actuating linkage connected to said lostmotion mechanism, rotary power means adapted for concurrent engagement with said actuating linkage and said lock actuating mechanism whereby rotation of said power source initially 10 unlocks said breaking strut prior to said actuating links overcoming the lost-motion in said lostmotion device and applying retractive force to said drag strut.

JOHN E. WESCOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,359,554 Griswold Oct. 3, 1944 2,374,146 Waters Apr. 17, 1945 

